Technical Field
This disclosure relates generally to optical nodes and more particularly, but not exclusively, to systems and methods for optical amplification of optical signals.
Description of Related Art
The statements in this section provide a description of related art and are not admissions of prior art. An optical amplifier is a device that amplifies an optical signal directly in the optical domain without converting the optical signal into a corresponding electrical signal. Optical amplifiers are widely used, for example, in the fields of optical communications.
One type of an optical amplifier is a doped-fiber amplifier, with a well-known example being the Erbium-doped fiber amplifier (EDFA). In operation, a signal to be amplified and a pump beam are multiplexed into the doped fiber. The pump beam excites the doping ions, and amplification of the signal is achieved by stimulated emission of photons from the excited dopant ions.
Another type of an optical amplifier is a Raman amplifier, which relies on stimulated Raman scattering (SRS) for signal amplification. A Raman amplifier uses the intrinsic properties of silica fiber to obtain signal amplification, such that transmission fibers themselves can be used as a medium for amplification, allowing the attenuation of data signals transmitted over the fiber to be mitigated within the fiber itself. More specifically, when a signal to be amplified and a pump beam are multiplexed into an optical fiber made of an appropriate material, a lower-frequency signal photon induces SRS of a higher-frequency pump photon, which causes the pump photon to pass some of its energy to the vibrational states of the fiber material, thereby converting the pump photon into an additional signal photon. An amplifier working on the basis of this principle is commonly known as a distributed Raman amplifier (DRA) or simply a Raman amplifier. The pump beam may be coupled into the fiber in the same direction as the signal (co-directional or co-pumping) or in the opposite direction (contra-directional or counter-pumping). The counter- and co-propagating Raman amplifiers are a marked improvement on this technology. In contrast to the standard Raman amplifier where a single counter-propagating Raman pump signal is responsible for the amplification of the traffic signals in the fiber, a counter-propagating and a co-propagating Raman amplifier may be used together. Together the co- and counter-propagating Raman pumps provide amplification to combat signal attenuation in fiber extending the reach of an optical span.
A multi-core fiber (MCF) increases a number of cores within a cladding of a single fiber. Multi-core fiber has the potential to increase data rates by using spatial division multiplexing (SDM). By increasing the number of cores within a single fiber, the information carrying capacity of the fiber is dramatically increased. Multi-core fibers have many times the signal-carrying capacity of traditional single-core fibers. Multi-core fibers may be employed in many applications ranging, e.g., from sensors to spatial division multiplexing to high density coupling.
A need exists for improved optical amplifiers to combat signal attenuation in multi-core fibers extending the reach of an optical span.